Various forms of electronic mice are known. A rudimentary form of electronic mouse is shown in German Offenlegungsschrift 1916348, and another example is shown in U.S. Pat. No. 3,987,685. Still other forms are marketed by Alps, Apple, and a number of other companies including the assignee of the present invention. Each of these electronic mice operate in what is fundamentally a very similar way, in that each employs a ball located within a housing such that the rotation of the ball causes generation of either an electrical, mechanical or optical indicia when the ball is rolled across a surface.
In conventional electronic mice, the ball is contained within the housing by various means, some of which include a plurality of wheels which frictionally engage the ball. Also in conventional systems, two of the friction wheels drive shaft encoders of any of various means. A third friction wheel, in the conventional arrangement, is loaded by means of a spring or otherwise to force the ball into engagement with the two wheels which drive the shaft encoders. Indicia of movement are generated by the shaft encoders operating along X and Y axes so that angular movements can be tracked with reasonable accuracy.
One of the major difficulties with electronic mice has been the requirement that the movement of the cursor on the screen accurately reflect the movement of the mouse across the chosen surface. During the initial stages of development of electronic mice, a fairly typical approach to meet this requirement was simply to provide a heavy steel ball as the rotational member.
After some further development, it was determined that coating the heavy steel ball with a material having a high frictional coefficient improved the performance of the mouse. Almost inexorably, the ball portion cf the mouse developed around the concept of a heavy steel ball coated by a friction inducing material in the belief that tis approach materially improved tracking. Improvements for tracking typically involved increasing the ball weight, or using a coating with a greater frictional coefficient.
However, the use of a heavy ball in the mouse is not without its limitations. One such limitation is that the heavy ball makes the mouse heavy to operate, which is a significant drawback in at least some applications. Another limiation is that the heavy ball is expensive, and the expense is significantly increased by the requirement for a frictional coating. These extra expenses are particularly significant because both the ball and the coating must be uniformly applied to provide uniform roundness needed for the best possible tracking.
In addition, the extra mass of steel or steel coated balls have created problems during shipping and usage. When a mouse having a massive ball is shipped with the ball already inside the ball cage, the shocks generated by the massive ball are capable of damaging the remainder of the mouse. In addition, in the event the mouse is dropped during usage, the massive ball is also capable of creating injurious shocks. The present invention lessens or eliminates these concerns, as will be appreciated from the following summary of the invention.